The Kapitän, Admiral and Diplomat B series models, also known as KAD B for short, were built from March 1969 to July 1977. In the opinion of some authors, they are the last upper-class models of the Opel automobile brand, which at the time belonged to the U.S. automobile group General Motors (GM), although Adam Opel AG itself sees things differently.

The exclusively four-door notchback sedans were available with inline six-cylinder or V8 gasoline engines with an output of 95 to 169 kW (129 to 230 hp). As with the predecessor KAD A series, all KAD B models have the same body shape. Until May 1970, the simplest, plainly equipped model – as with the KAD A series – was the Kapitän. The Admiral was the mid-range version. Opel also supplied the top model Diplomat with the V8 engine from the group’s sister company Chevrolet.

The new cars were several centimeters shorter and narrower than those of the KAD-A series. The body was smooth and bulky. Although it was more European than in the previous series, the US influences were still obvious and did not meet with the desired approval of potential buyers in Germany and Europe. The Kapitän and Admiral retained the wide rectangular headlights in the radiator grille, while the Diplomat received headlights in a vertical format. In the manner of the Mercedes W111, the turn signals sat behind their approximately square, curved diffusing lenses and the headlights in the somewhat protruding fenders. Also, the Diplomat’s taillights were smaller and narrower than those of the other two models. All had recessed windshield wipers.

The 2.8-liter inline-six experienced a minor power increase with modifications to the carburetor and exhaust system. Hydraulic tappets were also new. Furthermore, a fuel injection system developed together with Bosch was now optionally available for this engine. All KAD-B models received a complex and expensive De-Dion rear axle. This design weighed around 20 kg more than a simple rigid axle, but the unsprung masses were lower. This was to ensure good wheel control with lightly responding suspension. On request, all three models could be equipped with pneumatic level control, which increased the permitted towing capacity to 2000 kg (braked). In addition to crumple zones, a stable passenger cell and a generously trimmed interior, the safety equipment also included a safety steering column and a dual-circuit braking system with front disc brakes, brake booster and load-dependent brake force limiter. This series was also one of the first in Germany to have important body parts galvanized, which was intended to improve corrosion protection.

The Diplomat continued to be offered with the 2.8-liter inline six-cylinder engine with intake manifold injection and an output of 121 or 128 kW (165 or 175 hp) and the 5.4-liter Chevrolet eight-cylinder V-engine with 169 kW (230 hp), which was slightly improved over its predecessor. In keeping with the high top speeds attainable, versions with the V8 engine were equipped with four internally ventilated disc brakes.

Standard equipment included automatic transmission and power steering, while accessories included air conditioning, electric sunroof, leather interior and power windows, as well as mirrors adjustable from the inside, H4 halogen headlights and an electronic antenna integrated into the windshield (standard in the Diplomat from summer 1971).

In general, the Diplomat B was recognized by experts as a technically high-quality vehicle, but Opel’s market share in the luxury class nevertheless declined increasingly from the mid-1960s in favor of Mercedes-Benz and BMW, especially after Mercedes-Benz introduced the new S-Class (see Mercedes-Benz W116) in 1972. The first oil crisis of 1973 brought another significant slump, with production falling 90 percent to 1754 units in 1974 from 17,777 in 1969. The KAD series was therefore discontinued in July 1977.

Because of the low sales figures, the passing on of used cars into increasingly poorly maintained third hands and the passage of time of over 45 years, KAD models have now become extremely rare. Good, restored and well-maintained examples are therefore now traded at significantly higher prices than Mercedes models. The spare parts situation for the large Opel models is also comparatively much more difficult, which makes maintenance and possible repairs noticeably more expensive. Of the former entry-level Kapitän model, the rarest of the “big three” from the outset, only a few vehicles remain.